1. Field of the Invention
The invention relates to a control apparatus for a vehicle and a control method for a vehicle, and more specifically, relates to a control apparatus for a vehicle including a battery that is configured to be chargeable with regenerative electric power, and a control method for the vehicle.
2. Description of Related Art
For a battery that is mounted on a hybrid vehicle, an electric vehicle or the like, there has been proposed a charge control for protecting the battery from an excessive charging electric power. For example, in a case where a lithium-ion secondary battery is employed as the battery, there is known a phenomenon in which lithium ion in an electrolytic solution precipitates on an anode as lithium metal when an excessive electric current is input to the battery. For example, International Publication No. WO 2010/005079 discloses that an allowable value Ilim (a permissible input electric current value in International Publication No. WO 2010/005079) of the input electric current is set as the maximum of the input electric current that does not cause the precipitation of lithium metal (for example, see Paragraph [0022] in International Publication No. WO 2010/005079).
For protecting the battery, it is desirable to execute the feedback control of input electric current IB such that the absolute value of the input electric current IB to be detected by a current sensor does not exceed the allowable value Ilim. However, generally, there is a delay time in feedback control. Accordingly, when the input electric current IB is restricted after the input electric current IB reaches the allowable value Ilim, there is a possibility that the absolute value of the input electric current IB exceeds the allowable value Ilim and the battery cannot be adequately protected. Therefore, in consideration of the delay time in feedback control, a restriction target value Itag for which a predetermined amount of margin is secured relative to the allowable value Ilim is calculated (for example, see Paragraph [0030] in International Publication No. WO 2010/005079).
In International Publication No. WO 2010/005079, Kp×∫(Itag−IB)dt is calculated, using the difference value between the input electric current IB and the restriction target value Itag, and a coefficient Kp. As shown in the following Formula (A), the term is subtracted from a base electric power Winb that is a basis of the upper limit of charging electric power, and thereby, a permissible charging electric power value Win is set (see Paragraph [0053] in International Publication No. WO 2010/005079).Win=Winb−Kp×∫(Itag−IB)dt  (A)
However, International Publication No. WO 2010/005079 describes the coefficient Kp only as a feedback gain, and therefore, does not disclose a detailed configuration for setting the term (see Paragraph [0055] in International Publication No. WO 2010/005079). Accordingly, there is room to optimize the coefficient Kp.
More specifically, at the time of regenerative braking in a hybrid vehicle, an electric vehicle or the like, the regenerative electric power depending on the running situation of the vehicle is generated by a motor generator, and the battery is charged. When the absolute value of the permissible charging electric power value Win is set to an excessively small value, the charging electric power is strictly restricted, and as a result, there is a possibility that a sufficient regenerative electric power cannot be recovered. On the other hand, when the absolute value of the permissible charging electric power value Win is set to an excessive large value, there is a possibility that the battery is charged with an excessive electric power.